It is sometimes necessary in creating composite video signals to either add two video signals together or to allow the output of one video image generator to be operated on by another video image generator. Often two images can be combined by a simple addition, i.e., the video images being synchronously electronically combined or added at a single node. Simple signal addition may be suitable in many purposes, in particular if the two video sources which are to be combined have equivalent resolution for their necessary purposes. This simple addition of video signals is inadequate in other applications, particularly if one video signal is of a particular high quality and may suffer degradation because of the lesser quality of the secondary video signal.
Shown in FIG. 1 is a block diagram of the prior art method of adding a video micrometer video signal to an x-ray microscopy video output in commercial equipment sold by the assignee of the present invention. The x-ray microscope is, as its name implies, a device for creating an enlarged video image of very small substrates, and is commonly used in industries requiring detailed work at a microscopic level, such as in integrated circuit processing and assembly. In such work, and particularly for use with integrated circuit technology, it is desirable if on the video output of the x-ray microscope video image a field, or scale, or reference cursor, is placed onto the x-ray microscope video image. In the apparatus constructed as indicated in FIG. 1, the output image of the x-ray microscope is passed through a video micrometer before being displayed on a video display tube or monitor. The video micrometer electronically creates a video image of a moveable reticles and combines it with the video output from the x-ray microscope to create what is, in effect, an overlay over the x-ray microscope video image which is the output of the x-ray microscope. The video micrometer synchronizes the overlay with the video image based on the sync pulse contained in the composite video signal which it receives from the x-ray microscope. The video micrometer then adds its overlay image to the composite video and passes that to its output which, as illustrated in FIG. 1, goes directly to the appropriate monitor.
Unfortunately, as may often be the case with video imagery, the resolution of all components of a system made of many components may not be equivalent. In the case illustrated in FIG. 1, the video micrometer may have a video output of poorer resolution or may create a sync in its composite output which may be less sharp than the composite video output from the x-ray microscope. The result would be that the output video image of the x-ray microscope would be slightly degraded by the insertion of the video micrometer between it and the monitor. This is not a desirable situation, since the whole purpose of a microscope is to gain the maximum possible resolution and acuity in the image created.